At the outset, one should appreciate that, even in the health care field, where clarity may be crucial, confusion may exist in terminology in cases where similar words are used to refer to opposite conditions and or treatments. Whether this is due to a lack of knowledge, to carelessness, or to a different intent in meaning is immaterial. For our purposes, whe shall adhere to the following, which we believe to be standard nomenclature. Hypothermia is a condition of depressed or subnormal body temperature; hypothermia may be treated by using medication or it may be treated by exposing the patient to a hyperthermic (warmer than normal body temperature) environment. Some might refer to the latter treatment as hyperthermia, but we caution to avoid this usage. Hyperthermia is a condition of elevated body temperature; hyperthermia may be treated by using medication or it may be treated by exposing the patient to a hypothermic (cooler than normal body temperature) environment. Some might refer to the latter treatment as hypothermia, but we caution also to avoid this usage.
The use of external cooling means to treat patients with fever (or hyperthermia) is not new. U.S. Pat. No. 1,004,192, issued in 1911 to J. T. Phelan, teaches a cooling apparatus comprising a coolant-filled cooling pipe with closed ends connected to an elevated receptacle for liquid coolant and ice. The pipe is placed adjacent to the body and especially underneath the neck and surrounding the head of the supine patient. As the coolant in the pipes becomes warm, it will be replaced by cold coolant. Although Phelan does not discuss a motive force by which the warm coolant is replaced by cold coolant, his disclosure suggests that thermal convection currents are expected to accomplish this end. In contrast to the present invention, Phelan makes no suggestion that the liquid is not fully contained within the apparatus.
Along a similar vein, F. C. Hoore et el, in U.S. Pat. No. 3,867,939, issued in 1975, teaches a temperature-controlled applicator pad. A circuit of passages within this pad allows a thermal fluid to circulate into the pad, through a serpentine pattern of passages, and out of the pad in a forced circulation. Although the pad may be wetted, preferably with a sterile solution, to improve the heat transfer characteristics of the soft, absorbent, flexible covering, the thermal fluid is not the source of such wetting. In contrast to Moore, the present invention does not define a closed circuit for the flow of a thermal fluid; rather, the fluid water--is distributed to an absorbent sheet that provides yet greater dispersion of the water for contact with the skin of the patient, ultimately to be drained off to a receptacle for spent water.
Another such device for forced circulation of a thermal fluid through a fluid-tight circuitous path is presented in U.S. Pat. No. 4,996,145, issued in 1990 to M. Kikumoto et el. Designed primarily for use on wheelchairs and primarily for cooling the body of the wheelchair occupant, it teaches a pump cirulating a thermal fluid that is chilled by refrigeration.
U.S. Pat. No. 4,572,188, issued in 1986 to S. D. Augustine et el., teaches apparatus for controlling body temperature by means of a temperature-controlled gas mixture (usually air) supplied to an inflatable cover through which it circulates and which also serves as a plenum or manifold to transmit the temperature controlled gas to the body surfaces, thereby to thermally bathe the body in the gas. Because of the low volumetric heat capacity (measured in BTU/cu ft/degree F. or in Calories/liter/degree C.) of gases in general, and air in particular (about 1/3300 times that of liquid water), relatively large volumes of temperature-controlled gas are required to achieve the same effect of a quantity of water. The venting of the temperature-controlled gas in large quantity into the room in which the patient is being treated will thermally bathe the entire room and its other occupants in the temperature-controlled gas mixture. In contrast, the present invention uses water as a thermal medium; the use of water as a medium has little effect on the atmosphere in the room, largely because the spent water can be contained and does not present itself to other people in the room.
In U.S. Pat. No. 3,247,851, issued in 1966 to M. J. Seibert, an apparatus is taught for applying sustained moist heat to a human body by using an electrical heating jacket on an inverted bottle of a type commonly used for parenteral solutions, thereby to heat the liquid within, which is then applied by means of a drip line to moisten and to maintain an elevated temperature of a pad of adsorbent material. For extended moist heat treatment, unheated bottles may be connected in a series arrangement as may be commonly used for other purposes, but with the heated bottle being the final reservoir in the series.